1. Field of the Invention
The present invention relates generally to the field of four-wheel drive power transmission systems for vehicles, particularly to a system for lubricating the mating surfaces of an overrunning clutch and axleshafts, and more particularly to such systems that transmit power to the first of two sets of wheels while the wheel sets have the same speed, and to the other set of wheels when the speed of the first wheel set exceeds that of the other wheel set.
2. Description of the Prior Art
Drive mechanisms have been devised that transmit power to only one set of wheels when the four wheels of the vehicle are rotating at nearly the same speed. However, when the driven wheels begin to overrun, the nondriven wheels are driveably connected to the transmission and become driven, whereas the driving wheels in this condition are no longer supplied with power. Sometimes this action is done by providing the nondriven set of wheels with an overrunning clutch and by gearing the clutch such that it becomes engaged when a predetermined speed differential between the driving and nondriven wheels occurs. This requires that the overunning clutch be manually locked in order to obtain four-wheel drive when the vehicle is driven in reverse or when engine braking is required. Other systems use a conventional differential to allow the front and rear axleshafts to deliver power while rotating at different speeds. These systems generally require a manual lock-up device to prevent excessive wheel spin when encountering surfaces on which the wheels may slip.
Usually in mechanisms of this type, centrifugal force can be used as a medium for carrying lubricant from the sump to the surfaces of the clutch due to the action of the gear continuously rotating through the oil sump. However, the inner surfaces between the axleshafts and the inner races of the clutch to which the axleshaft is driveably connected, and surfaces adjacent the inner race that rotate at speeds relative to those of the inner race are not supplied with lubricant because these surfaces neither pass through the oil sump nor are they accessible to the outer surfaces on which the oil bath readily flows. Nonetheless, there is a need to protect mating surfaces that rotate at substantially different speeds continuously as the vehicle is driven.